This invention relates to a temperature threshold sensing circuit for an integrated circuit which comprises a semiconductor junction device providing a V.sub.BE reference and a resistor, a proportional-to-absolute-temperature (PTAT) current generator having a PTAT current source output connected in series with the resistor, the circuit further comprising means for detecting whether the voltage across the resistor exceeds the V.sub.BE reference and for generating an output signal which indicates whether the temperature of the integrated circuit is above or below a predetermined threshold temperature.
A circuit of the type set forth in the opening paragraph is known from U.S. Pat. No. 4,733,162. Such a circuit is useful, for example, for providing an over-temperature detection function in a power integrated circuit.
The semiconductor junction device in the circuit known from U.S. Pat. No. 4,733,162 is a bipolar transistor (referenced 29) whose base-emitter junction is connected in parallel with the resistor. The transistor (29) also acts as the detecting means by turning on and drawing a collector current when the PTAT voltage across the resistor exceeds V.sub.BE. The base current of the transistor in the known circuit detracts from the PTAT current, for which some compensation is provided by a further transistor (30), but the current through the detection transistor (29) is still not well-defined. This introduces uncertainty in V.sub.BE and hence also in the threshold temperature.
A further problem with the known circuit is that it requires bipolar transistors in both common emitter and common collector configuration, which may not be available in an integrated circuit when constructed using CMOS technology, for example. The range of device types and configurations available may be further restricted in a high-power integrated circuit because of isolation problems.